Use Rust in the Windows CI jobs

With v2.55.0, Git requires Rust by default, with an opt-out that is intended to be dropped in one of the next versions.

Due to the special circumstances in the Windows part of the CI builds, each Windows build job first downloads a "minimal Git for Windows SDK" that contains the GCC toolchain required to build and test Git. As a consequence, brian m. carlson opted out of Rust in Git's CI definition in 32d5b905909e (Enable Rust by default, 2026-04-09).

So: How could we stop opting out? Notably, Rust is not part of that minimal Git for Windows SDK, and including it would more than double that payload, which I consider prohibitive. Yet including Rust in the minimal Git for Windows SDK is not actually necessary, at least not for the GitHub workflow:
The runners on which this workflow is defined to run come with Rust pre-installed.

Granted, this Rust installation is configured to target the Windows-native C compiler, Visual C. To accommodate for the Windows CI job building with GCC, this patch series adds a step to the workflow that ensures that the needed Rust bits are installed and configured.

GitLab peeps, I still would love to ask for your help: I haven't been able to confirm that GitLab's Windows runners come with Rust preinstalled,
https://docs.gitlab.com/ci/runners/hosted_runners/windows/#available-runtimes
did not clarify that for me. Patrick (or anyone else with access to GitLab CI), could you see whether this patch series builds on saas-windows-medium-amd64 without need for further changes?

Changes since v3:

* Now including the "Changes since v2"... (I thought I had edited the PR comment, but either I forgot to press the "Update comment" button, or I missed one of the many issues I had today with PR comments, caused by many a 500).
* Removed the now-incorrect paragraph from the commit message that still talks about --target.
* Sending my humblest apologies for such a quick succession (but I really think that v3 is ready for next).

Changes since v2:

* Now using CARGO_BUILD_TARGET; Reworded the commit message accordingly.
* Dropped the now-unnecessary --target option.

Changes since v1:

* The inconsistency pointed out by Junio, that UCRT64 was once marked as using clang and once as using gcc was fixed by clarifying that UCRT64 uses GCC.

Johannes Schindelin (2):
rust: pick a GCC-compatible Cargo target under MSYS2/MinGW ci(windows): build with Rust

 .github/workflows/main.yml | 24 ++++++++++++++++++++++++
 Makefile                   |  2 +-
 ci/lib.sh                  |  3 ---
 config.mak.uname           | 25 ++++++++++++++++++++++++-
 4 files changed, 49 insertions(+), 5 deletions(-)

base-commit: f4742f3165d096130c39a71feb26374da37620f2
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-2213%2Fdscho%2Fuse-rust-in-windows-ci-builds-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-2213/dscho/use-rust-in-windows-ci-builds-v4
Pull-Request: https://github.com/gitgitgadget/git/pull/2213

Range-diff vs v3:

1: b70b001f62 ! 1: 6e8648b21c rust: pick a GCC-compatible Cargo target under MSYS2/MinGW
@@ Commit message
not defined in Git for Windows' minimal SDK that Git uses in its CI runs.

- Note that this _still_ requires an explicit --target option to be
- picked up in the way Git's build process calls cargo.
-

2: 76469029ff = 2: f6c2f52fb3 ci(windows): build with Rust

gitgitgadget